The present invention relates to a disc brake used in an automobile, and in particular, a disc brake apparatus in which an electric parking brake mechanism is incorporated.
Generally, a disc brake used in an automobile has: a pair of pads disposed on opposite sides of a disc; and a caliper adapted to move a piston forward, which is slidably disposed in a cylinder having a closed end, to press the pair of pads against and exert a brake force on the disc, when a hydraulic pressure is supplied by operation of a brake pedal. Recently, however, disc brakes further comprising electric parking brake mechanisms have come into practical use. A conventional example of a disc brake of this type is disclosed in Domestic Announcement No. HEI 05-506196 of PCT Application. This disc brake has a parking brake mechanism that uses an electric motor as a drive source disposed outside the cylinder to mechanically hold the piston, which is moved forward by a hydraulic pressure supplied into the caliper from the hydraulic circuit, in a braking position even after the hydraulic pressure is released.
The disc brake with the parking brake mechanism requires that a supply of a hydraulic pressure into the caliper be greater than the hydraulic pressure supplied during the parking brake operation, to ensure a smooth release of the parking brake. It is often the case that a driver is stepping on the brake pedal when operating the parking brake. In such a case, if the parking brake is operated while a hydraulic pressure higher than a predetermined pressure (a hydraulic pressure required to operate the parking brake) is supplied into the caliper by operation of the brake pedal, an even higher hydraulic pressure must be supplied into the caliper from the hydraulic circuit to release the parking brake. In other words, when the hydraulic pressure supplied into the caliper from the hydraulic circuit is required to be increased to a higher level, it takes as much time to reach that level and thus to release the parking brake.